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Systems Based on Lead Selenide
Published in Vasyl Tomashyk, 2 Semiconductors, 2022
PbSe2O5 is thermally stable up to 380°C ± 10°C and decomposes at the heating to 500°C with formation of PbSeO3 (Markovskiy and Sapozhnikov 1960). It also crystallizes in the monoclinic structure with the lattice parameters a = 451.5 ± 0.1, b = 950.3 ± 0.3, c = 1161.8 ± 0.2 pm, β = 90.33 ± 0.01°, and a calculated density of 5.93 g⋅cm−3 (Koskenlinna and Valkonen 1995) [(an experimental density was determined to be 5.35 ± 0.02 g⋅cm−3 (Markovskiy and Sapozhnikov 1960)]. The title compound was prepared by the precipitation of amorphous PbSeO3 from an aqueous solution of Pb(NO3)2 with selenous acid (Koskenlinna and Valkonen 1995). The precipitate was added to a concentrated (>1.0 M) aqueous solution of SeO2 with a stoichiometric ratio of Pb to SeO2 of 1:2. Well-formed crystals with yellowish tint were grown by allowing the suspension to stand at temperatures between 57°C and 100°C for a few days. PbSe2O5 could be also obtained as a result of the heating of Pb(HSeO3) at a temperature higher than 130°C (Markovskiy and Sapozhnikov 1960).
Industrial minerals
Published in Francis P. Gudyanga, Minerals in Africa, 2020
Commercially, elemental selenium is produced from selenide anode mud as a by-product in the electrolytic refining of sulphide ores such as copper, nickel and lead. The industrial production of selenium is via the extraction of selenium dioxide from the residues during the purification of copper. The residue is oxidised by sodium carbonate to produce the selenium dioxide which is then mixed with water and the solution is acidified to form selenous acid in the oxidation step. Selenous acid is reduced to elemental selenium [624,625] by bubbling it with sulphur dioxide. The power necessary to operate the electrolysis cells is significantly decreased during the electrowinning of manganese by addition of selenium dioxide [626]. The current production of copper is a combination of solvent extraction and electrowinning (SXEW) altering the availability of selenium as only a comparably small part of the selenium in the ore is con-leached with copper [623].
Feedstock Preparation
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
Other processes include the Alkazid process for removal of hydrogen sulfide and carbon dioxide using concentrated aqueous solutions of amino acids. The hot potassium carbonate process decreases the acid content of natural and refinery gas from as much as 50% to as low as 0.5% and operates in a unit similar to that used for amine treating. The Giammarco-Vetrocoke process is used for hydrogen sulfide and/or carbon dioxide removal. In the hydrogen sulfide removal section, the reagent consists of sodium carbonate (Na2CO3) or potassium carbonate (K2CO3) or a mixture of the carbonates which contains a mixture of arsenite derivatives and arsenate derivatives; the carbon dioxide removal section utilizes hot aqueous alkali carbonate solution activated by arsenic trioxide (As2O3) or selenous acid (H2SeO3) or tellurous acid (H2TeO3). A word of caution might be added about the last three chemicals which are toxic and can involve stringent environmental-related disposal protocols.
Selenium in soil-microbe-plant systems: Sources, distribution, toxicity, tolerance, and detoxification
Published in Critical Reviews in Environmental Science and Technology, 2022
Anamika Kushwaha, Lalit Goswami, Jechan Lee, Christian Sonne, Richard J. C. Brown, Ki-Hyun Kim
Anthropogenic activities lead to the release of Se to the atmosphere and eventual deposition to ecosystems. Three groups of Se compounds have been identified in the atmosphere: volatile organic compounds (dimethyl selenide [DMSe], dimethyl diselenide [DMDSe], and methaneselenol), volatile inorganic compounds (Se dioxide), and Se0, which is linked to ash or particles. DMSe is a stable compound. Hydrogen selenide and Se dioxide are unstable in air. Hydrogen selenide is oxidized into Se and H2O. Se dioxide is transformed into selenious acid in moist conditions. In nature, Se is closely associated with sulfur-containing minerals, pyrites, and fossil fuels (Mehdi et al., 2013) which collectively account for 50–65% of atmospheric Se emissions (Sharma et al., 2015) through natural processes such as weathering and soil leaching (Sathe et al., 2020). Figure 1 depicts the sources of Se and its route of entry into soil-plant-microbial systems. Approximately 37–40% of the total Se is released into the atmosphere due to anthropogenic activities (Wen & Carignan, 2007). The burning fossil fuels (e.g., coal) releases large amounts of Se in ash, volatile compounds, and liquid effluent (Bañuelos et al., 2020). Mining activities release Se when mined rocks are exposed to snow, rain, and variation in temperature (Song et al., 2020). Other anthropogenic activities such as metal refining, industrial waste disposal, and agriculture also release Se as a by-product (Goswami et al., 2019, 2017; Nancharaiah & Lens, 2015; Santhosh et al., 2020).